Octa-1,3,6-trienes

An active catalytic species in the dimerization reaction is Pd(0) complex, which forms the bis-7r-allylpalladium complex 3, The formation of 1,3,7-octa-triene (7) is understood by the elimination of/5-hydrogen from the intermediate complex 1 to give 4 and its reductive elimination. In telomer formation, a nucleophile reacts with butadiene to form the dimeric telomers in which the nucleophile is introduced mainly at the terminal position to form the 1-substituted 2,7-octadiene 5. As a minor product, the isomeric 3-substituted 1,7-octadiene 6 is formed[13,14]. The dimerization carried out in MeOD produces l-methoxy-6-deuterio-2,7-octadiene (10) as a main product 15]. This result suggests that the telomers are formed by the 1,6- and 3,6-additions of MeO and D to the intermediate complexes I and 2. 

Electrocyclic reactions of 1,3,5-trienes lead to 1,3-cyclohexadienes. These ring closures also exhibit a high degree of stereospecificity. The ring closure is normally the favored reaction in this case, because the cyclic compound, which has six a bonds and two IT bonds, is thermodynamically more stable than the triene, which has five a and three ir bonds. The stereospecificity is illustrated with octatrienes 3 and 4. ,Z, -2,4,6-Octatriene (3) cyclizes only to cw-5,6-dimethyl-l,3-cyclohexadiene, whereas the , Z,Z-2,4,6-octa-triene (4) leads exclusively to the trans cyclohexadiene isomer. A point of particular importance regarding the stereochemistry of this reaction is that the groups at the termini of the triene system rotate in the opposite sense during the cyclization process. This mode... 

Figure 30.3 Electrocyclic interconversions of 2,4,6-octa-triene isomers and 5,6-dimethyi-1,3-cyclohexadiene isomers.

The male-produced volatiles eficiting responses from male and female antennae of the sap beetle, Colopterus truncatus Randall (Coleoptera Nitidulidae), were identified as (2A ,4A ,6A )-3,5-dimethyl-2,4,6-octa-triene, 2E, AE, 6T )-4,6-dimethyl-2,4,6-nonatriene and 2E, AE,6E,SE) 3,5,7-trimethyl-2,4,6,8-decatetraene. A fourth male-specific compound... 

Dupont and co-workers studied the Pd-catalyzed dimerization [108] and cyclodimerization [109] of butadiene in non-chloroaluminate ionic liquids. The biphasic dimerization of butadiene is an attractive research goal since the products formed, 1,3,5-octatriene and 1,3,6-octatriene, are sensitive towards undesired polymerization, so that separation by distillation is usually not possible. These octa-trienes are of some commercial relevance as intermediates for the synthesis of fragrances, plasticizers, and adhesives. Through the use of PdCl2 with two equivalents of the ligand PPhj dissolved in [BMIM][Pp6], [BMIM][Bp4], or [BMIM][CF3S03], it was possible to obtain the octatrienes with 100 % selectivity (after 13 % conversion) (Scheme 5.2-23) [108]. The turnover frequency (TOP) was in the range of 50 mol butadiene converted per mol catalyst per hour, which represents a substantial increase in catalyst activity in comparison to the same reaction under otherwise identical conditions (70 °C, 3 h, butadiene/Pd = 1250) in THF (TOP = 6 h ). 

The reaction of isoprene with MeOH catalyzed by Pd(acac)2 and Ph3P is not regioselective, giving a mixture of isomers[37]. However, l-methoxy-2,6-dimethyl-2,7-octadiene (35), the head-to-tail dimer, was obtained in 80% yield, accompanied by the tail-to-tail dimer (15%) using 7r-allylpalladium chloride and BU3P. On heating, 35 was converted into 2,6-dimethyl-l,3,7-octa-triene (36) by an elimination reaction[38]. 

Dimethylamino-2.3,4,5-tetrafluo-ro- EI0b2, 267 (l-NR2-2,3,4,5-F4 - [Pg.863]

The chemistry of cyclooctatetraene is interesting and unusual. Particularly noteworthy is the way in which it undergoes addition reactions to form products that appear to be derived from the bicyclic isomer, bicyclo[4.2.0]2,4,7-octa-triene, 8. In fact, there is an electrocyclic equilibrium between cyclooctatetraene and 8 (Section 21-10D) and, although the position of equilibrium lies... 

Rule 3. If two double bonds are present, the ending of the name will be diene if three double bonds are present, the ending will be triene. These endings replace the ending ane in the name of the saturated fundamental chain for euphony, the letter fta sometimes precedes these endings — for example, the name octane for the eight-carbon fundamental chain becomes octadiene for dihydromyrcene (No. 3, Chart 3) and octa triene for allo-ocimene (No. 5, Chart 3). 

Complex 105 cydizes with DMAD to give the diastereomeric bound bicyclo[2.2.2]octa-trienes 109A and 109B in a 1 1 ratio (Scheme 14). Oxidation of these complexes liberates the corresponding triene 110 as well as the disubstituted anisole 111, presumably generated with acetylene from the cycloreversion of 110. 

Methoxycarbonylcyclopropane derivatives are also obtained in 38% yield (cis.trans = 30 8) by the reaction of l-methylbicyclo[1.1.0]butane with methyl acrylate in the presence of a catalytic amount of [ RhCl(norbomadiene) 2], in addition to 2-methyl-1,3-butadiene (37%) and 2,7-dimethyl-l,4,7-octa-triene (25%). ... 

The reaction of bis(trifluoromethyl)tetramethylbicyclo[2.2.2]octa-triene with Mo(C0)6 (343) and of tetrafluorobenzobicyclo[2.2.2]octa-triene with Cr(CO)g (575) aifords the yellow (olefin)M(CO)3 complexes with structures comparable to these of the analogous cobalt (168) and iron (136) complexes, respectively. 

Since electronic excitation changes the symmetries of HOMO and LUMO, it also changes the reaction stereochemistry. (2E,4 )-Hexadiene, for example, undergoes photochemical cyclization by a disrotatory path, whereas the thermal reaction is conrotatory. Similarly, (2E,4Z,6k)-octa-triene undergoes photochemical cyclization by a conrotatory path, whereas the thermal reaction is disrotatory., ... 

Tetrafluor- (benzo-tri- cyclo[2.2.2]octa- trien-(2,5,7)) l%ige Losung in Pentan/Aceton (96 4) 450 W Hg-Mitteldruck-lampe Quarz, 66% Umsatz F 7,8,9,10- Tetrafluor-(ibenzo-cycloocta-telraen) Spur 1... 

Triazines react with tricyclo[4.2.2.02,5]deca-3,7,9-triene-7,8-dicarboxylates in refluxing toluene to yield azocines 18 via the given intermediates400,401 (see Section E. 1.1.1.1.1.). In the absence of aryl groups in the 5- and 6-positions of the 1,2,4-triazines, polycyclic compounds are isolated, probably by reaction of the dienophile with the formed azabicyclo[4.2.0]octa-trienes,402 the valence tautomers of the azocines, or with the initially formed polycyclic intermediates. 

Rearrangements have also been observed in D-allo- and D-manno-pyranosides, in certain cyclo-octa-triene and -tetraene derivatives, and in the cleavage of the 1,3-photoadduct between cyclobutene and benzene. ... 

COT is prepared by the polymerization of ethyne at moderate temperature and pressure in the presence of nickel salts. The molecule is non-planar and behaves as a typical cyclic olefin, having no aromatic properties. It may be catalytically hydrogenated to cyclo-octene, but with Zn and dil. sulphuric acid gives 1,3,6-cyclooclairiene. It reacts with maleic anhydride to give an adduct, m.p. 166 C, derived from the isomeric structure bicyclo-4,2,0-octa-2,4,7-triene(I) ... 

Abbreviations acac, acetylacetonate Aik, alkyl AN, acetonitrile bpy, 2,2 -bipyridine Bu, butyl cod, 1,5- or 1,4-cyclooctadiene coe, cyclooctene cot, cyclooctatetraene Cp, cyclopentadienyl Cp, pentamethylcyclopenladienyl Cy, cyclohexyl dme, 1,2-dimethoxyethane dpe, bis(diphenyl-phosphino)ethane dppen, cis-l,2-bis(di[Atenylphosphino)ethylene dppm, bis(diphenylphosphino) methane dppp, l,3-bis(diphenylphosphino)propane eda,ethylenediamine Et,ethyl Hal,halide Hpz, pyrazole HPz, variously substituted pyrazoles Hpz, 3,5-dimethylpyrazole Me, methyl Mes, mesityl nbd, notboma-2,5-diene OBor, (lS)-endo-(-)-bomoxy Ph, phenyl phen, LlO-phenanthroline Pr, f opyl py, pyridine pz, pyrazolate Pz, variously substituted pyrazolates pz, 3,5-dimethylpyrazolate solv, solvent tfb, tetrafluorobenzo(5,6]bicyclo(2.2.2]octa-2,5,7-triene (tetrafluorobenzobanelene) THE, tetrahydrofuran tht, tetrahydrothicphene Tol, tolyl. 

Rappoport, Z. Kobayashi, S. Stanger, A. Boese, R. Crystal structure of l,2-diphenyl-5,7-di-/er/-butylspiro[2.5]octa-l,4,7-trien-6-one, a possible model for diphenylvinylidene-phenonium ions. J. Org. Chem. 1999, 64, 4370-4375. 

Again, the bicyclic valence isomer coexists in sufficient concentration, that the bicyclic peroxide 19 was readily accessible in ca. 20% yield. Alternatively, the thermally labile bicyclic valence isomer of cyclooctatetraene, namely bicyclo[4.2.0]-octa-2,4,7-triene, was converted into the corresponding endoperoxide on low temperature singlet oxygenation and reduced with diimide to yield 19. 

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